1. Field of the Invention
The present invention relates to a catalyst for preparing an alkenyl aromatic compound by dehydrogenating an alkyl aromatic compound wherein CO2 is present in a molar ratio of approximately 0.015 to 0.20.
2. Description of the Related Art
Styrene, which is an alkyenyl aromatic compound, is an important industrial material widely used as a material for the production of polystyrene, acrylonitrile butadiene styrene (“ABS”) resin or synthetic rubber. Styrene is industrially produced by reacting ethylbenzene under dilute conditions mainly by means of a catalyst having an iron oxide and an alkali metal, in particular potassium, as main components in an insulation type-dehydrogenation reaction which is doubly or triply arranged in series. However, the dehydrogenation reaction of ethylbenzene to the styrene monomer is an equilibrium reaction, and thus the reaction is largely prevented by the generated hydrogen. Also, because the dehydrogenation reaction is endothermic, the temperature decreases as the reaction proceeds, which is disadvantageous with regard to the rate of reaction. For at least these reasons, it is difficult to obtain styrene in a high yield using production equipment in which the above-mentioned dehydrogenation reactors are arranged in series.
As described in “Petrochemical Process,” (2001), p 86, Ed. The Japan Petroleum Institute; U.S. Pat. No. 4,565,898; and Japan Patent No. H05-38800, it has been proposed that the hydrogen generated from the dehydrogenation reaction of ethylbenzene to the styrene monomer can be selectively oxidized by means of oxygen and thus partially removed, resulting in the equilibrium of the reaction shifting to the product, with the heat of the oxidation reaction compensating the decreasing temperature by the dehydrogenation reaction. However, in such a process, oxygen added in the oxidation step partially reacts with hydrocarbons other than hydrogen to generate CO2. The dehydrogenation catalyst disposed in the downstream oxidation step is generally used as the catalyst having iron oxide and potassium as main components, and as described in Catalyst 29:8 pg. 641 (1987) and Petrotech 29:3 pg. 158 (2006), CO2 results in a significant decrease in the conversion and selectiveness of the dehydrogenation catalyst. Therefore, this results in an industrial disadvantage.
In yet another improvement of the dehydrogenation catalyst of ethylbenzene, when the reaction in which a conventional preparation process, i.e. a preparation process which comprises diluting ethylbenzene without the oxidation step is carried out under a mild condition such that less CO2 is generated, a variety of improved process are proposed, for example, a modification of the composition in catalyst as described in Japan Patent Nos. JP-A H03-11812 and JP-A S64-45320, as well as a variation in a pore size distribution of a material as described in Japan Patent No. 3881376. However, it has not previously been proposed to use the high-yield dehydrogenation catalyst under a specific reaction condition, for example, in the presence of highly-concentrated CO2 which is employed in the dehydrogenation step disposed in the downstream oxidation step as above-mentioned.
Description Of the Related Art Section Disclaimer: To the extent that specific publications are discussed above in this Description of the Related Art Section, these discussions should not be taken as an admission that the discussed publications (for example, published patents) are prior art for patent law purposes. For example, some or all of the discussed publications may not be sufficiently early in time, may not reflect subject matter developed early enough in time and/or may not be sufficiently enabling so as to amount to prior art for patent law purposes. To the extent that specific publications are discussed above in this Description of the Related Art Section, they are all hereby incorporated by reference into this document in their respective entireties.